<template>
  <ul class="list">
    <li
      class="item"
      v-for="item of letters"
      :key="item"
      :ref="item"
      @touchstart.prevent="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
      @click="handleLetterClick"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props:{
    cities:Array
  },
  computed:{
    letters(){
      const letters=[]
      for(let i in this.cities){
        letters.push(i)
      }
      return letters
    }
  },
  data(){
    return{
      startY:0,
      touchStatus:false,
      timer:null
    }
  },
  updated(){
    // this.startY=this.$refs['A'][0].offsetTop
    this.startY=this.$refs['A'][0].offsetTop
  },
  methods:{
    handleLetterClick(e){
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart(){
      this.touchStatus=true
    },
    handleTouchMove(e){
     if(this.touchStatus){
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer=setTimeout(()=>{
          const touchY=e.touches[0].clientY-79
          const index=Math.floor((touchY-this.startY)/20)
          if(index>=0&& index<this.letters.length){
             this.$emit('change',this.letters[index])
          }
        },16)
       
     }

    










      // const touchY=e.touches[0].clientY-79
      // const index=Math.floor((touchY-this.startY)/20)
      // if(index>=0 && index<this.letters.length){
      //   this.$emit('change',this.letters[index])
      // }
     



    },
    handleTouchEnd(){
      this.touchStatus=false
    }

  }
}
</script>

<style lang="stylus" scoped>
  @import '~@/assets/styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
